How can I implement the call rejection function when the line is busy?

Issue description

When initiating a call invitation, if the callee already has an incoming call or is answering a call from another user, how can I implement such a scenario with the call invitation function of the Agora RTM SDK?

SDK function description

The call invitation function of the Agora RTM SDK only implements the basic logic in a call invitation, such as canceling, accepting, or refusing a call invitation. A call invitation is only the beginning of a call; it ends when the call begins. To implement a real-world call scenario, you must use both the Agora RTM SDK and an audio-and-video SDK, such as the Agora RTC SDK.

Implementation

Agora recommends using two flags (at the app level) to listen for each user's states. For example, you can use inviteState to indicate whether the user is in a call invitation and callState to indicate whether the user is in a call. The initial state of both flags is false. A user with either of the flags being set as true cannot receive a new call invitation.

1. Ensure that your project has implemented the Agora RTM SDK and an audio-and-video SDK, such as the Agora RTC SDK.
2. When a user receives the onRemoteInvitationReceived callback triggered by the Agora RTM SDK, set the inviteState flag as true:
   • When receiving the following callbacks, set theinviteState as false to indicate that the call invitation has ended but the call will not begin, and then skip the following steps.
     • onRemoteInvitationRefused: The user has declined the call invitation;
     • onRemoteInvitationCanceled: The call invitation has been cancelled;
     • onRemoteInvitationFailure: The cal invitation ends in failure.
   • When a user receives the onRemoteInvitationAccepted callback (the user has accepted an incoming call invitation), set the inviteState as false and callState as true to indicate that the call invitation has ended and the call is about to begin.
3. Listen for the connectionState state through the onConnectionStateChanged callback triggered by the Agora RTC SDK:
   • If connectionState is at any of the following state, set the callState flag as true to indicate that the user is setting up a call or is in a call:
     • CONNECTING: The user is setting up a call;
     • CONNECTED: The call connection is set up;
     • RECONNECTING: The call is being re-established.
   • If connectionState is at any of the following state, set the callState flag as false to indicate the user is not in a call:
     • DISCONNECTED: The call is disconnected;
     • FAILED: The call ended in failure.
4. Refer to the table above to judge whether a user is busy. If a user is busy, call refuseRemoteInvitation provided by the Agora RTM SDK and set the response property within the received RemoteInvitation object as "busy".